RU2490781C1 - Double-balanced frequency converter - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: double-balanced frequency converter has two balanced frequency converters, input, heterodyne and output circuits, a 180° phase section, three pairs of interfaced phase changers; the output of the input circuit is connected to inputs of the first pair of interfaced phase changers, the outputs of which are connected to corresponding signal inputs of the pair of balanced frequency converters, heterodyne inputs of which are connected to corresponding outputs of the second interfaced pair of phase changers; the output of one of the balanced frequency converters is connected to the input of one phase changer of the third pair of interfaced phase changers, the outputs of which are connected to the input of the output circuit; the output of the other balanced frequency converter is connected to the input of the 180° phase section, the output of which is connected to the input of the other phase changer of the third pair of interfaced phase changers.

EFFECT: high degree of suppressing sideband components in the high-frequency range.

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Description

The invention relates to the field of radio engineering and can be used in broadband receiving devices that are part of microwave radio monitoring equipment.

Modern multichannel radio receivers operate in a wide range of input signal frequencies in some cases exceeding several octaves. To effectively suppress “mirror” channels, reduce the analysis time of radio signals and simplify the equipment, the input range of such devices is usually divided into several subbands of which the signal frequencies are converted by the heterodyning method down along the frequency axis to the range of the first intermediate frequencies, which in turn can also be divided into subbands etc. [1.2].

Known frequency converters intended for use in multi-channel radio receivers operating in a wide frequency range of input signals [3]. The electrical circuit of such a converter is shown in figure 1. The converter contains input 1, heterodyne 2 and output 3 circuits, as well as a semiconductor diode D1.

The disadvantage of such frequency converters is the possibility of getting into the output (intermediate) frequency band of the combination frequencies and the frequencies of the harmonic components of the input and heterodyne signals. This leads to a narrowing of the dynamic range of the receiving device and to limiting the width of the output frequency ranges of the converters. For example, the width of the output frequency ranges in multichannel broadband receivers cannot exceed one octave due to the possibility that the combination frequencies multiple of the second harmonic of the input signals get into them.

Known balanced and double balanced frequency converters, performing in the process of frequency conversion suppression of combination components and harmonics. Various options for circuits of such frequency converters are given in the book [3]. The electrical circuits of the most widely used converters are shown, respectively, in FIGS. 2 and 3. FIG. 2 shows a diagram of a balanced converter. The converter contains an input circuit 1, a local oscillator circuit 2 and an output circuit (intermediate frequency circuit) 3, as well as semiconductor diodes D1, D2. Figure 3 shows a diagram of a double balanced transducer. The converter contains an input circuit 1, a local oscillator circuit 2 and an output circuit (intermediate frequency circuit) 3, as well as semiconductor diodes D1, D2, D3 and D4.

The combination frequencies are determined from the known relation f _k = | mfc ± nfg | [3], in which the coefficients m and n are integers of the natural series of numbers: 0, 1, 2, 3, 4 ..., f _c and f _g are the frequencies of the signal and the local oscillator. Coefficients m correspond to harmonics of input signals, and n - harmonics of heterodyne signals. Depending on the values of the coefficients of the type, the combinational components corresponding to these combinational frequencies are distributed between the input, output and heterodyne circuits [3].

The coefficients m and m also determine the order of the combination components equal to the sum of the absolute values of these coefficients. Knowing the order allows you to approximately evaluate the relative levels of the combination components, which decrease with increasing order of the combination component. Therefore, in the design of microwave receivers in each case, the maximum permissible value of the orders of combinational components is set, the frequencies of which fall into the output (intermediate) frequency ranges of the converters. Typically, the maximum value is limited to sixth or seventh order.

We introduce the notation for the even and odd Raman frequencies, respectively, m ”, n” = 0, 2, 4, 6 ... and m ', n' = 1, 3, 5 ... In a double balanced frequency converter, the circuit of which is shown in FIG. .3, combinational components with frequencies | m'fc ± n'fg | excite only output circuits (intermediate frequency circuits) 3, combinational components with frequencies | m'fc ± n ”fg | only signal circuits 1 are excited, and combinational components with frequencies | m ”fc ± n'fг | excite only heterodyne chains 2 [3]. Raman components with frequencies | m ”fc ± n” fg | do not excite any of the above chains [3]. Thus, the combination components of non-exciting output circuits (intermediate frequency circuits) will be suppressed. In the case considered, these are combinational components with frequencies | m'fc ± n ”fg |, | m” fc ± n'fg | and | m ”fc ± n” fg |.

Note that in the considered frequency converter (see Fig. 3), the input (signal) 1, heterodyne 2 and output 3 circuits are always isolated from each other. This allows you to change the purpose of these circuits. For example, you can make circuit 2 signal, and circuit 1 heterodyne, or make circuit 2 output, circuit 1 signal, and circuit 3 heterodyne. The latter option is convenient for "conversion up", when the conversion with the output signal frequency f _c + f _{g is} used as the main one.

A double balanced frequency converter consists of two balanced converters connected in a certain way to each other. Figure 4 shows a diagram of a double balanced converter (figure 3) in the form of a connection of two identical circuits of balanced converters, the electrical circuit of which is shown in figure 2.

In the microwave range, double balanced frequency converters can be implemented using strip, microstrip, and slotted transmission lines (see, for example, [4]), as well as using coaxial and waveguide transmission lines (see, for example, [5] and [6 ]). In accordance with the diagram in figure 4, figure 5 shows the structural diagram of a double balanced microwave converter, adopted as a prototype. As balanced converters, it uses orthomodic balanced frequency converters [5], the electrical circuit of which is shown in figure 2. A double balanced frequency converter contains an input (signal) circuit 1, a local oscillator circuit 2, and an output circuit (intermediate frequency circuit) 3, as well as balanced converters 4 and 5. Figure 5 shows the heterodyne waveguide circuit 2 conventionally. Between the balanced transducer 5 and the branch point of the output circuit 3, a phase section 6 is turned on 180 °, which is necessary for phasing the signals coming into circuit 3 and providing isolation between circuits 1-3. As in the circuit of FIG. 4, in the circuit of FIG. 5, the input (signal) 1, heterodyne 2, and output 3 circuits are decoupled from each other.

The disadvantage of a double balanced frequency converter - prototype, the structural diagram of which is shown in figure 5, is the small value of the suppression of the combinational and harmonic components of the input and heterodyne signals in some cases not exceeding 20 ... 30 dB, which is a consequence of the non-identical electrical parameters of semiconductor diodes and geometric sizes of diode cameras. This leads to a limitation of the width of the dynamic range and the width of the ranges of the output frequencies of the converters.

Common features of the prototype and invention: a double balanced frequency converter containing two balanced frequency converters 4 and 5, input 1, heterodyne 2 and output 3 circuits and phase section 6 to 180º, and the output of one balanced frequency converter 5 is connected to the input of phase section 6 to 180º

An object of the invention is to increase the degree of suppression of the combination components in the output frequency range of double balanced frequency converters in order to expand the dynamic range and range of output frequencies and, ultimately, reduce the number of subbands (channels) of the receiving device containing these double balanced frequency converters in a given frequency band of input signals.

The problem is solved by dividing the double balanced frequency converter into two balanced converters, and introducing into it pairs of conjugate phase shifters included between the balanced converters and the branch points of the input, heterodyne and output signal circuits.

An additional introduction to the input, output, and local oscillator circuits of the known double balanced frequency converters of the conjugated pairs of phase shifters allows using these phase shifters to compensate for the difference in phase difference of the combination components f _to , formed simultaneously in both balanced frequency converters, from 180º or from zero, which solves the problem .

The invention is illustrated by drawings.

Figure 1 shows the electrical circuit of the frequency converter (analogue).

Figure 2 shows the electrical circuit of a balanced frequency converter (analogue).

Figure 3 shows the electrical circuit of a double balanced frequency converter (analogue).

Figure 4 shows the electrical circuit of a double balanced signal frequency converter, composed of circuits of two balanced signal frequency converters (analogue).

Figure 5 shows the structural diagram of a double balanced frequency converter - prototype.

Figure 6 shows the structural diagram of a double balanced frequency converter according to the invention.

Figure 7 shows the construction of a double balanced signal frequency converter according to the invention.

In the figures, the notation is introduced: 1 - input (signal) path; 2 - heterodyne path; 3 - output path (intermediate frequency path); 4 and 5 - balanced signal frequency converters; 6 - phase section at 180º; 7 and 8, 9 and 10, 11 and 12 - conjugated pairs of phase shifters; 13 - valve.

The technical result of the invention is achieved due to the fact that the double balanced frequency converter (Fig.6) contains: input (signal) circuit 1, local oscillator circuit 2, output circuit (intermediate frequency circuit) 3, two balanced frequency converters 4 and 5, phase section 6 with a phase shift of 180º and three pairs of conjugate phase shifters: the first 7 and 8, the second 9 and 10 and the third 11 and 12.

The output of input circuit 1 is connected to the inputs of the first pair of coupled phase shifters 7 and 8, and their outputs are connected to the corresponding signal inputs of a pair of balanced frequency converters 4 and 5, the heterodyne inputs of which are connected to the corresponding outputs of the second pair of phase shifters 9 and 10, the inputs of which are connected to the output of the heterodyne circuit 2. In addition, the signal output of one balanced frequency converter 4 is connected to the input of one phase shifter 11 of the third pair 11 and 12 of the paired phase shifters, the outputs of which are connected s to an input of the output circuit 3, the balanced output of another inverter 5 is connected to the input of the phase section 6 to 180º, whose output is connected to another input of the phase shifter of the third pair of phase shifters coupled.

Depending on the implementation method, balanced converters can be made in the form of a combination of strip, microstrip, and slotted transmission lines [4] or coaxial and waveguide transmission lines [5]. For example, in the latter case, the input circuit 1 and the output circuit 3 (Fig.6) are made in the form of coaxial lines, and the heterodyne circuit 2 in the form of a waveguide transmission line.

The phase section 6 can be performed, for example, due to the difference in the electric lengths of the segments of the transmission lines between the balanced converters 4 and 5 and the associated phase shifters 11 and 12 in the output circuit 3 (Fig.6).

As coordinated phase shifters, for example, coaxial transmission lines with a variable length can be used [7]. In such phase shifters, consisting of two segments of coaxial lines, using the collet joints mounted on the external and internal conductors, one segment is moved relative to the other without breaking contact between the external and internal conductors. In this case, the length of the transmission line composed of the two above-mentioned segments is changed. Since the total electric length of the sliding lines is determined by their geometric lengths, a change in the same geometric length of two identical phase shifters leads to the same change in their electric lengths. In this way, pairing of these phase shifters is achieved.

The input circuit 1 of the double balanced frequency converter through the coupled phase shifters 7 and 8 is connected to the signal inputs of the balanced frequency converters 4 and 5, and the local oscillator circuit 2 through the coupled pair of phase shifters 9 and 10 are connected to the heterodyne inputs of the balanced converters 4 and 5. Output circuit 3 through the phase shifter 11 is connected to the output circuit of the balanced transducer 4 and through cascade-connected phase shifter 12 and the phase insert 6 with the output circuit of the balanced transducer 5 (Fig.6).

Dual balanced frequency converter operates as follows. The input and heterodyne signals f _c and f _g pass through circuits 1 and 2 to balanced converters 4 and 5. As a result of the simultaneous action of these signals, currents with combinational frequencies f _k = | mfc ± nfg | flow through semiconductor diodes. The meaning of the type coefficients was explained above. The phases of the currents of pairs of combinational components at the outputs of converters 4 and 5 (varying with a frequency f _k ) are either the same or differ by 180º, which is determined by the phase difference between the input and heterodyne signals supplied to the semiconductor diodes, and the values of the coefficients m and n. Depending on the values of the phase differences of these currents, the combinational components formed in the balanced converters are added up either in output 3, or in signal 1, or in heterodyne 2 circuits [3]. Since the absolute value of the type coefficients of a useful output signal is equal to unity, currents with odd coefficients add up only in the output circuits.

In real double balanced frequency converters, due to the non-identical electrical parameters of semiconductor diodes and the geometric dimensions of the diode chambers, the relative phases of the same combination components formed in converters 4 and 5 may differ from zero or from 180º. This leads to incomplete compensation of antiphase combinational components at the branch points of circuits 1, 2, and 3, as well as to incomplete addition of in-phase signals at the same points. As a result, the suppression coefficients of the Raman components with frequencies | m'fc ± n ”fg |, | m” fc ± n'fg | and | m ”fc ± n” fg | in the corresponding chains are reduced.

Using conjugated phase shifters, phase errors are compensated for due to the non-identical electrical parameters of the semiconductor diodes and the geometric dimensions of the diode chambers, which will increase the suppression of undesirable combination components. With the synchronous adjustment of each phase shifter of the conjugated pair to the same magnitude, the reaction of the corresponding circuit to the main signal and to the combination component will be different. For example, in the input signal circuit 1, such a tuning will not have a significant effect on the passage of the input signal, since the phase difference of the signals entering the balanced converters 4 and 5 will not change during synchronous tuning of the phase shifters. The combinational components with frequencies | m'fc ± n ”fg | arrive at the branch point of path 1 in antiphase. During the reconstruction of the conjugated pair of phase shifters 7 and 8, the phase of the reflection coefficient for these combinational components will change and, consequently, the load resistances in the plane of semiconductor diodes at the frequencies of these combinational components will change. Thus, the restructuring of the phase shifters will affect the matching of the semiconductor diodes with the output path 3 at the frequencies of this combinational component and, therefore, the amplitude of this combinational component in the output circuit. Similar processes will take place in other paths. By reconstructing the desired pair of conjugated phase shifters, you can configure them so that the amplitude of the undesirable combination component is minimal, which solves the problem.

As an example, consider a receiver operating in the frequency range 28.0 ... 40.0 GHz. The first conversion is carried out in the range of the first intermediate frequencies of 4.0 ... 8.0 GHz. The average frequency of the output range is 6 GHz. At a given average frequency, the width of the output range cannot exceed 4.0 ... 8.0 GHz, because otherwise, the combination frequency 2f _with -2f _g will fall into it. Therefore, the input frequency range is divided into three sub-bands: 28.0 ... 32.0 GHz, 32.0 ... 36.0 GHz and 36.0 ... 40.0 GHz, each of which, provided f _s > f _g, has its own local oscillator frequency 24.0 GHz, 28.0 GHz and 32.0 GHz respectively.

Using the property of double balanced frequency converters described above, the number of subbands and, therefore, the number of channels of the receiving device can be reduced. For example, the number of channels can be reduced to two 28.0 ... 34.0 GHz and 34.0 ... 40.0 GHz, if you expand the first range of output frequencies to 4.0 ... 10.0 GHz. The local oscillator frequencies in this case will be equal to 24.0 GHz and 30.0 GHz.

In this case, in the output frequency band of the first sub-band (28.0 ... 34.0 GHz), in addition to the frequency of the useful signal f _s -f _g , the combination frequencies 2f _s -2f _g , 3f _g -2f _s and 3f _s -4f _g fall, and in the output frequency band of the second sub-band (34.0 ... 40.0 GHz), the combination frequencies 2f _s -2f _g , and 3f _s -4f _g . The double balanced frequency converters according to the invention, made according to the circuit of FIG. 6, additionally suppresses combinational components with the above frequencies using conjugated pairs of phase shifters. To suppress the combinational component with a frequency of 2f _s -2f _g , any conjugate pair of phase shifters can be used. To suppress the combination component with a frequency of 3f _g -2f _s , either a pair of phase shifters included in the input circuit 1 or in the output circuit 3 or both pairs can be used. To suppress the combinational component with a frequency of 3f _with -4f _g , either a pair of phase shifters included in the heterodyne circuit 2 or in the output circuit 3 or simultaneously in both pairs can be used. Note that the amplitude of the combinational component with a frequency of 3f _with -4f _{g is} quite small, because it has a high order of 7. In most practical cases, this component is not additionally suppressed.

The considered method of additional suppression of combinational components and harmonics is especially effective in the case of up-conversion, when the conversion with the output signal frequency f _s + f _{g is} used as the main one. With this transformation, the main obstacle to the operation of the receiving device is the harmonics of the input and local oscillator signals, which can be significantly suppressed in the considered circuits. To implement this option in the circuit of Fig. 6, we change the purpose of circuits 2 and 3, namely, we swap the output and heterodyne circuits. Now circuit 2 will be output (intermediate frequency circuit), and circuit 3 heterodyne. The purpose of the input circuit 1 is not changed. Note that the circuit 2 is waveguide (Fig.6), which also represents certain convenience in the implementation of the "conversion up".

Consider this option as an example of converting the frequencies of the input signals from the range of 9.0 ... 11.0 GHz to the frequency range of 17.0 ... 19.0 GHz with a LO frequency of 8.0 GHz. In the output (intermediate frequency) band, combinational frequencies up to 7 orders of magnitude are not included, with the exception of the second harmonic of the input signal 2f _s , the amplitude of which can be reduced with the help of conjugated phase shifters 9 and 10 included according to the scheme of Fig. 6.

The technical result of the invention is achieved due to the fact that the double balanced frequency converter for implementing the method according to the diagram in Fig.6 contains: two balanced frequency converters 4 and 5, paths 1,2 and 3, a phase section of 180º 6, a pair of paired phase shifter 9 and 10. The device should operate in the operating frequency range of the input signals 9.0 ... 11.0 GHz, which are converted into the output frequency range 17.0 ... 19.0 GHz. The frequency of the local oscillator signal is 8.0 GHz. The operating frequency bands of the input and output signals are limited by the second harmonic of the 2fc input signal, due to which they narrow two times, respectively, to 9.0 ... 10.0 GHz and 17.0 ... 18.0 GHz.

The design of a double balanced frequency converter is shown in Fig.7. It is similar to the design of the double balanced transducer described in the patent [6]. As balanced frequency converters, orthomode converters described in the patent [5] can be used. As input (signal) circuit, circuit 1 is used, circuit 3 is used as output circuit, and circuit 2 is used as heterodyne circuit. For additional suppression of the second harmonic of input signals, one pair of conjugated phase shifters 9 and 10 is sufficient. The output circuit is made in the form of a H- waveguide tee type (see, for example, [8]). The phase insert 6 (Fig.6) is implemented due to the different lengths of the arms of the chain 2.

A metal valve 13 is introduced into the output waveguide circuit 3 of the double balanced frequency converter, the height of which is equal to the height of the narrow wall of the waveguide. The valve is a continuation of the inner narrow walls of the waveguide tee. The gate end located inside the output waveguide is the summation point of the radio signals coming from balanced frequency converters 4 and 5. Useful output signals (signals with intermediate frequencies) arrive at the summation point with the same phases. Therefore, the movement of the gate valve 13 does not affect the parameters of the output signal after summing at the output 3. The second harmonics of the input signal generated in the converters 4 and 5 enter the output waveguides in antiphase. Therefore, when moving the valve 13, the distance from the summation point to the diodes of the converters 4 and 5 will change, and accordingly, the load resistance at the second harmonic frequency will change. Thus, the position of the valve 13 can be selected at which the amplitude of the second harmonic of the input signal in the output circuit 3 of the double balanced frequency converter will be minimal.

A mock double balanced frequency converter was made. An experimental study of the converter confirmed that by moving the gate valve, the second harmonic suppression of the signal can be increased by more than 70 dB.

The technical result of the invention is achieved: the dynamic range of the receiving device is expanded by an additional 50 ... 70 dB; in the required signal frequency band, the number of subbands (channels) of the receiving device is reduced from 3 to 2.

Distinctive features of the invention.

Three pairs of coupled phase shifters are introduced into the converter, the output of the input circuit (1) connected to the inputs of the first pair of coupled phase shifters (7 and 8), and their outputs connected to the corresponding signal inputs of a pair of balanced frequency converters (4 and 5), the heterodyne inputs of which are connected with the corresponding outputs of the second conjugated pair of phase shifters (9 and 10), the inputs of which are connected to the output of the local oscillator circuit (2), in addition, the signal output of one balanced frequency converter (4) is connected to the input of one phase shifter of the switch (11) of the third pair (11 and 12) of conjugated phase shifters, the outputs of which are connected to the input of the output circuit (3), and the output of the phase section (6) is 180º, connected to the input of another phase shifter (12) of the third pair of conjugated phase shifters.

Literature

1. Hofmann C., Baron A. Wideband ESM Receiving System, Part II. "Microwave Journal", No. 2, 1981, pp. 57, 58, 60, 61.

2. Harper T. The trend toward hybridization in modern surveillance receivers. Communications International, 1981, No. 9, pp. 38, 43, 44, 47.

3. M.E. Movshovich. "Semiconductor frequency converters." “Energy”, Leningrad Branch, 1974, p. 244, 245.

4. V.N. Oleinikov, V.V. Boykov, V.A. Lukyanchuk. "Double balanced microwave mixer." Communication technology. Radio measuring equipment. Issue 7 (32), 1980, Moscow, pp. 56-64.

5. US patent No. 3638126.

6. US patent No. 3932815.

7. "Transmission lines of centimeter waves" / Ed. G.A. Remeza. Soviet Radio, Moscow, 1951, vol. II, p. 77.

8. Ya.D. Shirman. "Radio waveguides and cavity resonators." Moscow, Svyazizdat, 1959, Article 324.

Claims (1)

A double balanced frequency converter containing two balanced frequency converters, an input, local oscillator and output circuits and a 180 ° phase section, the output of one balanced frequency converter being connected to a 180 ° phase section input, characterized in that three pairs of conjugated phase shifters are introduced into the converter moreover, the output of the input circuit is connected to the inputs of the first pair of paired phase shifters, and their outputs are connected to the corresponding signal inputs of a pair of balanced frequency converters, heterodyne in the odes of which are connected to the corresponding outputs of the second conjugated pair of phase shifters, the inputs of which are connected to the output of the heterodyne circuit, in addition, the signal output of one of the balanced frequency converters is connected to the input of one phase shifter of the third pair of coupled phase shifters, the outputs of which are connected to the input of the output circuit, and the phase output 180 ° sections are connected to the input of another phase shifter of the third pair of conjugate phase shifters.

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